2436 Storage and other scope has large signal void in 100ms roll up to 20ms

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Antman
Posts: 3
Joined: December 7th, 2016, 8:59 am
Country: United States

2436 Storage and other scope has large signal void in 100ms roll up to 20ms

Post by Antman » December 7th, 2016, 9:54 am

Hello,

2436 50Mhz storage scope and other brands produce near similar results:

Can it be possible for a 12.5Khz (80us) aliased PWM signal produce a void (125ms) in ADC sample data when rolling (100ms) or static 20ms? I think this void is actually 2.5khz(400us) which would be above the ADC sampling rate of the channel so it ends up as aliased blank time. Even though the rolling digital signal CH1 is heavily aliased the analog current monitor has a transient response (CH2) seems to concur PWM pulse frequency shifted well below 12.5khz in the void area. CH2 is the trigger source.

What say the world; Is a 12.5Khz BFO able to create an burst IF (2.5khz) and not be captured or even visible at 50us horizontal, remain stealth?
BFO: Beat frequency oscillator, (This case synchronous gating 12.5Khz PWM, for 100ms becomes asynchronous to the PWM clock source)
IF: Intermediate frequency

Thanks in advance for providing any real thought on this complex signal issue.
TM4C-PWM-Delay.jpg
TM4C-PWM-Delay.jpg (142.89 KiB) Viewed 10126 times
Last edited by Antman on December 7th, 2016, 12:54 pm, edited 1 time in total.

Antman
Posts: 3
Joined: December 7th, 2016, 8:59 am
Country: United States

Re: 2436 Storage and other scope has large signal void in 100ms roll up to 20ms

Post by Antman » December 7th, 2016, 12:53 pm

Here is another capture 125ms void of the same 80us PWM signal CH1. Guessing void could result from asynchronous PWM oscillator gating in an otherwise synchronous pulse train. Perhaps that causes a phase shift at a higher aliasing frequency and the void thus occurs. Does that sound about right or are all these strorage scopes missing the reason for doing a time roll in the first place?
TM4C-PWM-Delay2.png
TM4C-PWM-Delay2.png (24.59 KiB) Viewed 10122 times

Antman
Posts: 3
Joined: December 7th, 2016, 8:59 am
Country: United States

Re: 2436 Storage and other scope has large signal void in 100ms roll up to 20ms

Post by Antman » December 14th, 2016, 4:13 pm

Perhaps it is time for storage scopes to somehow indicate FOR (frequency out of range) in the signal area of a compression void. I don't like the word alias being used by some engineers simply to jump to the conclusion the voided area and entire capture is not even valid.

Might some how a secondary trace zoom window pop up to show FOR pulses ? versus no pulses compressed aliased void signal area. Something was occurring to PWM CH1, looked like 2.3-3.3Khz was bursting 10 second intervals inside 12.5Khz PWM but the differential was to great to show at 100ms or even 20ms.

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